These vets are not going to be intimidated. They speak for all the families who were devestated by Kerry AND McCain's failure with regard to the POW issue.
McCain could have overcome attacks from vets. To non-vets, the sniping and infighting doesn't have a lot of impact. It's like the Shaq / Kobe feud. Most fans would rather they just stop carping and focus on the game at hand.
For the most part, McCain was running on his record as a Senator, his reputation as a "maverick" and on his signature issue of campaign finance reform.
The reason McCain lost is that Campaign Finance Reform is now and was then a complete dud. Nobody understands Campaign Finance Laws. Nobody cares about them when they're broken. If anyone did, then Bill Clinton and Al Gore would have lost in landslides.
With Kerry, he is not running on his record as a Senator, and he does not have a signature issue beyond "I'm not George W. Bush". Frankly, that's the only issue any of his voters care about.
If Kerry is torpedoed by the Swift Boat Veterans, it will be more for the way he reacted to them than the specific charges leveled against him.
Kerry is handling this very, very, very badly. He's had nothing but harsh words directed at Bush for 2 years. He claims he will fight a more effective, smarter, and sensitive War On Terror. Yet in his greatest moment of crisis, he calls out to George W. Bush as THE ONLY MAN IN THE WORLD powerful enough to stop these attacks.